1. Field of the Invention
The present invention is directed to an apparatus for accurately measuring the weight of a fluid flowing through a pipeline, and more particularly to an apparatus for accurately measuring the varying density of a slurry flowing through a pipeline. The present invention is also directed to an apparatus capable of measuring the flow velocity of a slurry flowing through a pipeline.
2. Brief Description of the Prior Art
Pipelines capable of transporting coal and various other mined minerals such as iron ore, in the form of a thick aqueous slurry have been known for a long time. These pipelines, particularly coal slurry pipelines, are presently gaining increasing importance in view of the world's increasing reliance on coal as a major energy source.
Such slurry pipelines for coal and other minerals vary greatly in length and diameter. The particulate size of the slurried coal or other solid mineral may also vary depending on the purpose and particular application of the transporting pipeline. In some instances the slurry predominantly contains rather fine particulate matter, while in some others the slurry may include relatively large, "chunk" sized particles. In case of coal slurry pipelines, the slurry may contain as much as 50% solid material by volume. As it is well known in the prior art, the density of slurries having rather large solid particles is usually not uniform throughout any cross-section of the pipeline; rather the heavier particles are settled toward the bottom of the pipeline. Furthermore, the average density of the slurry passing through any given cross section of the pipeline often varies as a function of time.
In light of the above, it has become standard practice in the art to determine the amount of coal or other solid mineral passing through any given point on the pipeline by measuring and monitoring the average density of the slurry as a function of time. This is accomplished in the prior art either by use of nuclear densitometers or by devices which measure the weight of a given pipe section containing the slurry flowing therethrough. Both nuclear densitometers and the weight measuring type densitometers, however, suffer from certain inherent shortcomings.
Nuclear densitometers work rather poorly when the density of the slurry is not uniform throughout the cross section of the pipe. The prior art weight measuring type densitometers on the other hand, are, generally speaking, unable to accurately determine the true weight of a given pipe section because of the inherent structural problem that the pipe section must be physically coupled to the pipeline. Various types of flexible joints were used for this purpose in the prior art, and such prior art density or weight measuring devices are described in U.S. Pat. Nos. 3,503,267; 3,320,791; 688,388; 2,039,997; 2,613,530; 2,669,118; 3,812,723; 3,143,887 and 1,905,558.
The joints of these prior art devices, however, negatively affect the accuracy of the measured weights and densities because of their usually nonlinear bending stiffness. The above cited patents indicate that significant effort was devoted in the prior art to increase the accuracy of weight measuring type densitometers, and that, in spite of this effort, truly accurate measurements have, up to the present, not been possible.